The present invention relates to a plastic encapsulated semiconductor device wherein a semiconductor chip mounted on a lead frame is encapsulated together with inner leads in a plastic resin and a manufacturing method therefor. More particularly, it relates to a method of implementing a plastic encapsulated semiconductor device with a thinner profile and higher reliability.
As more semiconductor devices have been mounted on a mother substrate in a higher density, miniaturization and a thinner profile have been required of a recent semiconductor product to be mounted on the mother substrate. To implement a miniaturized semiconductor device with a thinner profile, a TAB technique using a plastic tape has been developed. A thin-profile semiconductor device may also be implemented by using a lead frame instead of the TAB technique. For example, there has been developed a single-side plastic encapsulated semiconductor device wherein only one side of the lead frame provided with a semiconductor chip is sealed with a sealing resin.
Referring to FIG. 11, a conventional single-side plastic encapsulated semiconductor device will be described.
As shown in the drawing, a semiconductor chip 103 is mounted on a die pad 102 of a lead frame 101. An electrode of the semiconductor chip 103 is electrically connected to inner leads 104 of the lead frame 101 via thin metal wires 105. The semiconductor chip 103, die pad 102, inner leads 104, and thin metal wires 105 are sealed with a sealing resin 106 only on the top side of the lead frame 101 provided with the semiconductor chip 103.
In the plastic encapsulated semiconductor device shown in FIG. 11, outer leads 107 serving as external electrodes are arranged on the bottom face of the semiconductor device, while only the side of the lead frame 101 provided with the semiconductor chip 103 is sealed with the sealing resin 106. Since the back side of the lead frame 101 is not substantially sealed, a thin profile is achieved. Tip portions 104a of the inner leads 104 of the lead frame 101 are formed to have tapered profiles to exhibit sufficient adhesion to the sealing resin 106.
The conventional single-side plastic encapsulated semiconductor device shown in FIG. 11 is manufactured by the following procedures.
First, the tip portions 104a of the inner leads 4 are formed to have tapered profiles by mechanical or chemical processing. Then, the semiconductor chip 103 is bonded onto the die pad 102. Subsequently, the electrode of the semiconductor chip 103 is electrically connected to the inner leads 104 by means of the thin metal wires 105. Thereafter, the side of the lead frame 101 provided with the semiconductor chip 103 is sealed with the plastic resin 106 by transfer molding. Final processing such as the bending of the outer leads 107 protruding from the sealing resin 106 is performed to complete the manufacturing of the plastic encapsulated semiconductor device.
FIG. 12 shows another conventional single-side plastic encapsulated semiconductor having a structure different from that of the plastic encapsulated semiconductor device shown in FIG. 11.
As shown in FIG. 12, an insulating plastic tape 108 for interconnecting the individual inner leads 104 of the lead frame 101 is provided to function as a die pad for carrying the semiconductor chip 103. After the semiconductor chip 103 is mounted on the plastic tape 108, the electrode of the semiconductor chip 103 is electrically connected to the inner leads 104 by means of the thin metal wires 105. Thereafter, the semiconductor chip 103, the inner leads 104, and the thin metal wires 105 are sealed with the sealing resin 106 on the side of the lead frame 101 provided with the semiconductor chip 103.
The plastic encapsulated semiconductor device shown in FIG. 12 has the advantage of achieving a thinner profile over the plastic encapsulated semiconductor device shown in FIG. 11. In contrast to the plastic encapsulated semiconductor device shown in FIG. 11 wherein the semiconductor chip 103 is mounted on the die pad 102 having the top face substantially flush with the top faces of the inner leads 104, the inner leads 104 and the semiconductor chip 103 are mounted on the plastic tape 108 in the plastic encapsulated semiconductor device shown in FIG. 12. Accordingly, the difference in level between the top faces of the inner leads 104 and the top face of the semiconductor chip 103 is smaller in the semiconductor device shown in FIG. 12 than in the semiconductor device shown in FIG. 11, so that the sealing resin 106 has a smaller thickness in the semiconductor device shown in FIG. 12. As a result, the whole plastic encapsulated semiconductor device has a reduced thickness.
To achieve a thinner profile, however, only one side of the lead frame 101 provided with the semiconductor chip 103, i.e., the top side of the lead frame 101 is substantially in contact with the sealing resin 106 in each of the conventional semiconductor devices shown in FIGS. 11 and 12. The arrangement reduces a contact area between the lead frame 101 and the sealing resin 106 and impairs adhesion therebetween, leading to degraded reliability of the final product.
Moreover, since only one side of the lead frame 101 is substantially sealed with a plastic resin, a stress in the sealing resin 106 may adversely affect the semiconductor chip 103 or cause cracking in the sealing resin 106 composing a package.